The present invention relates to a printer, facsimile apparatus, copier or similar electrophotographic image forming apparatus using a developer in the form of toner or a toner and carrier mixture. More particularly, the present invention relates to a toner recycling mechanism included in an image forming apparatus for collecting and conveying toner removed by a cleaning device.
An image forming apparatus of the kind described often includes a toner recycling mechanism for collecting and conveying toner removed from a photoconductive element or similar member by a cleaning device for recycling it or for disposing of it.
Generally, a collected toner conveying device is constructed to transfer the toner collected by the cleaning device to either one of a developing device or a collected toner storing device arranged independently of the cleaning device. The collected toner conveying device may include a tubing connecting the toner outlet of the cleaning device to the collected toner storing device. The tubing has a coil screw thereinside for conveying the collecting toner to the storing device. Alternatively, the storing device may be positioned in the vicinity of the toner outlet of the cleaning device, so that the collected toner may be transferred to the storing device mainly by gravity.
To convey a developer, toner or similar powder, use may be made of a screw, a paddle or a bucket in relation to a developing section or a toner feeding section included in the developing device. Alternatively, use may be made of a screw pump generally referred to as a Mono pump and capable of transferring powder without resorting to a coil screw.
However, the conventional tubing and coil screw scheme has the following problems (1)-(8) left unsolved.
(1) The coil screw must be extended to a position close to the toner storing device or the developing device.
(2) To insure the rotation of the coil screw, the toner transfer path should preferably be linear or gently curved, i.e., it should not be sharply bent. This limits the layout and makes it difficult to design the apparatus. Further, the collected toner storing device should preferably be positioned below the toner outlet of the cleaning device, further limiting the layout of the apparatus.
(3) A heavy frictional load acts between the coil screw and the tubing and increases the torque necessary for the rotation of the coil screw. This limits the distance over which the collected toner can be conveyed, renders the construction bulky, and complicates the construction of the apparatus.
(4) It is difficult to insure durability and to promote easy maintenance.
(5) Due to the limitation on the position of the collected toner conveying device, the apparatus body is increased in overall size, sophisticated in construction, and increased in cost.
(6) The toner storing device or the developing device must be arranged substantially integrally with the cleaning device, limiting the position of the device as to mounting and limiting the amount of toner that can be stored. As a result, the collected toner conveying device is applicable only to a low speed machine and a user-oriented copier/printer expected to produce only a small number of copies or printings.
(7) The capacity, configuration, material and so forth of the collected toner storing device have critical influence on the manual operation relating to toner collection, maintenance, and delivery cost of the collected toner from the user to the manufacturer.
On the other hand, the screw pump scheme is attracting increasing attention and can implement a toner collecting and conveying device free from the problems of the above coil screw and tubing scheme. Specifically, the screw pump provides the developing device and therefore the apparatus body with an adequate size and insures the quality, performance and function of the cleaning device.
However, the problem with the screw pump is that a stator included therein is formed of rubber and caused to wear or creep by a rotor contacting it due to aging. Consequently, the amount of bite of the rotor and stator into each other and the degree of close contact decrease, lowering the delivery pressure of the screw pump. The stator is therefore a part to be replaced and increases the service cost.
Technologies relating to the present invention are disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 9-288397, 10-69167, 10-49025, 10-26875, 10-20636, and 5-27650.